Process for dewaxing mineral oils



Patented Nov. 26, 1940 UNITED "STATES PROCESS FOR DEWAXING MINERAL onls Sijbren Tijmstra,

Berkeley, and Donald S.

McKittrick, Oakland, Calif., assignors to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing. Application June 20, 1936, Serial No. 86,353

2 Claims.

This invention relates to a process for separating various waxy substances from mineral oil containing the same. More particularly, it pertains to an improved diluent for decreasing the viscosity of the oil and the solubility of the wax, while improving the solubility of the oil in the liquid phase produced when solid wax is separated from oil, whereby the wax and the oil are separated more readily than has been possible heretofore. This application is a continuation-in-part of our copending application Serial No. 735,626, filed July 17, 1934, which has now' matured into Patent No. 2,191,136, dated Feb.

Mineral oils naturally contain varying amounts of waxy hydrocarbons, often designated as paraffin wax or petrolatum, and hereinafter generically designated as waxes, which at normal or elevated temperatures are dissolved in the liquid hydrocarbons, hereinafter referred to as oil, but which solidify or become extremely viscous at lower temperatures; If these oils are to be used as lubricants at these reduced, temperatures the solidified or highly viscous wax causes the oil to resist flow. When the wax content is too low to impede flow, it may, nevertheless} cause cloudiness in the oil. It becomes necessary,

therefore, to effect-the removal of all or some of the wax.

The first step in such a process is the creation of conditions under which the wax has a minimum solubility in the phase containing the oil. This Wax probably contains aliphatic hydrocarbons and/or naphthenic and other hydrocarbons; it belongs to the group of components of petroleum which are the least soluble in selective solvents. The removal of wax may be accomplished by any of several methods.

In accordance with oneof these methods, the oil is chilled to a temperature substantially below that at which the wax'solidifies and the wax is separated from the liquid oil by mechanical means. As an improvement in such a process, it is common to add a non-selective diluent, such as liquefied, normally gaseous hydrocarbons, light naphthas, etc., to the oil to reduce its viscosity and facilitate the mechanical separation.

In another method, a selective solvent medium is added to the initial oil, and the wax-free components of the initial oil are dissolved therein. This method necessitates the use of a solvent medium which is sufficiently selective to dissolve the oil at a suitable dewaxing temperature without dissolving the wax. The ordinary selective solvents which are employed for example in liquid-liquid solvent extraction processes to dissolve certain types of oils which are less paraffinic in nature from those which are more parafiinic in nature are not in general suitable for use as solvent media, because in dewaxing processes the solventis used to dissolve the desired oil which,-in the case of extraction processes, it is desired to recover in the liquid phase insoluble in the solvent.

Certain of such selective solvents may, however, be employed for dewaxing purposes by adding thereto a quantity of a secondary solvent, sometimes referred to as a solubility enhancing solvent. The addition of the secondary solvent improves the miscibility of oil and selective solvent, but in most cases destroys the selectivity of the resulting mixture between wax and oil, so that the resulting mixture of primary selective solvent and solubility enhancing solvent is to a great extent equivalent to a non-selective diluent, andfunctions only to reduce the viscosity of the chilled oil.

We have discovered that carbon substituted derivates of furane containing at least one polar substituent, such as -OH, --Cl-IO, -COOI-I, -COOR, ROI-I, R(OI-I).R', RCHO, RCOOH, --RNH2, RX (where R stands for an alkyl radical and X stands for halogen and halogen substituted derivatives thereof, which are liquid at dewaxing temperatures in the presence of oil as well as'those which become liquid upon the addition of a solubility enhancing agent, are particularly suitable for dewaxing mineral oils. We have, further, found that improved results may be obtained by using these furane derivatives together with one or more solubility enhancing agents. These furane derivatives show a high selectivity between oil and wax, although diluted with solubility enhancing agents. Specific examples of suitable furane derivatives are: furfural, furfuryl amine, furfuryl diamine, furfuryl chloride, methyl furfuryl ether, and n-propyl furyl carbinol. Of these, furfural is the most desirable, since it possesses the best solvent characteristics.

These selective solvents may be employed with any suitable enhancing agent which is a good solvent both for oil, and for the selective solvent although the solubility enhancing solvent need not be completely miscible with the selective solvent or with the oil in all proportions. Any one or a mixture of many substances may be used as secondary or solubility enhancing solvents, but they should preferably be selected from those solvents which themselves have a low solvent fairly selective solubility enhancing solvent is employed. For example, butyl alcohol usually gives'better results than hexane, cyclo-hexane, or benzol. Y

Numerous specific examples of solubility enhancing solvents are given in the said parent application. It includes, inter alia, aliphatic alif solvent mixtures may often be mixed with the oil cohols, aldehydes, ethers, ketones, allcontain; ing between four and twelve carbon'atoms such as primary and secondary butyl alcohols, butyr aldehyde, diethyl ketone, hexan'one, diethyl ether, diethyl thioether, as well as numerous other compounds, such as carbon'bisulfide, all phatic amines, esters of lower fatty acids and lower aliphatic alcohols containing more thanfour and less than thirteen carbon atoms, branched chain and cyclic aliphatic hydrocar bons, aromatic hydrocarbons, etc.

While the furane derivatives may be employed with any solubility enhancing solvent, we have foundthat there exists a class of solubility enhancing agents which is peculiarly adapted for use in connection with these particular selective solvents. This class consists of aliphatic aldehydes containing from four to twelve carbon atoms, and halogenated derivatives of hydrocarbon gases containing from one to five carbon atoms, and particularly the 1,2 dichlor derivatives of aliphatic hydrocarbons having from two to five carbon atoms. The aliphatic chains may be straight or branched chain. Examples of this preferred group of solubility enhancing solvents are: Butyraldehyde, octylaldehyde, chloro form, ethylene dichloride, propylene dichloride, diand tri-chlorethylenes, butylene dichloride, and 1,1 dichlor butane. Suitable solvent mixtures may, for example, consist of from 10 to 65% of a substituted furane such as furfural and from 35 to 90% of a solubility enhancing solvent. 7

The method which is the subject of our invention relies primarily on the peculiar properties of the above mixtures of solvents, which were found to create a condition in which there is a large difference between the solubility of the solid or waxy components of the initial oil and the solubility of the liquid or oil components thereof. In one-aspect, our methodcomprises the steps of mixing a waxy oil, such as lubricating oil, fuel oil, etc., which may be either a residual or a distillate-oil, with our selective solvent and solubility enhancin solvent, and chilling the resulting mixture to a dewaxing temperature to solidify the wax, which ma then be separated from the liquid portion of the system by any mechanical means, such as filtration, cold settling, or centrifuging, depending upon the character of the wax. Our process is, however, particularly suitable fcr filtration methods. The dewaxing temperature may, for example, be slightly below the melting point of the lowest melting wax which it is desired to remove. The pour point of the dewaxed oil may in certain cases be slightly higher than the dewaxing temperature, but by adjusting the proportions of selective solvent and solubility enhancing solvent, as described below, pour points which are as much as 20 F. below the dewaxing temperature may be obtained.

It is desirable, although not essential, to produce a homogeneous wax-oil-solvent system prior I to the precipitation step. To achieve this, the

from 65 C. to 100? C., or higher, and then cool- 'ing it slowly to the dewaxing temperature. When the mixture is initiallywarmed, it is necessary to cool the oil-solvent mixture, and this may be eifected by indirect cooling or auto-refrigeration.

Where very low pour points are not essential, our

at ordinary temperatures of the order of 18 C., 'thereby'obviating the necessity of chilling the oil. The chilling, when used, is not only for the purpose of merely freezing out the wax, as in theprocesses now practiced, but also for the purpose of increasing the selectivity of the solvent which the wax'is caused to separate by mere mixture which may have been added to the oil at chilling, and anon-selective solvent or diluent is added to reduce the viscosity of the'oil and to expedite the separation of the solidified wax. In this connection it should'be noted that the above selective solvents become more selective atlower temperatures. V i

Under certain conditions the wax which is precipitated according to .the procedure outlined above, either with or without chilling during-precipitationcmay be so soft as to make itsseparation diificult. It is in these cases advantageous to chill the precipitated wax during or just prior to its final removal to harden it. Subsequently the solvent mixture is removed from the separated liquid by any means. such as distillation.

To be filterable or otherwise separable from the. il-solvent phase, the wax particles must be of suitable form, size and strength and/or hard ness. We have found that if in precipitating the wax a very small amount of liquid oil is separated out from the oil with the wax crystals, clusters of crystals are formed and the separation of wax from'the solution of oil and solvent is facilitated. The amount. of oil necessary for this purposedepends upon the size of the'initial wax crystals,

and it is frequently practical to permit substantially no. oil to be separated out with the wax. Since the separation of an excess quantity of oil reduces the yield of dewaxed oil, it is desirable to control the amount of the'oil which is separated with the wax, as described below. V a I A convenient method' of controlling this amount of oil is to regulate the concentration of the solubility enhancing solvent in the solvent mixture. The necessary dilution ratio, i. -e., the ratio of the combined solvent mixture to the initial oil, is generally determined by theviscosit of the oil and the solvent mixture and by the selectivity of the solvent mixture at the dewaxing temperature, and is made as low as possible with a view of conserving the solvent. When using the new solvent mixtures of our invention, the dilutionratio may be much lower than the ratio employed with the known solvent mixtures- For example,wehaveobtainedexcellent results when using a dilution ratio of 2:1, and even lower ratios, such as 1:1 may be employed, although we prefer to employ ratios of about'4: 1. At very low temperatures, ratios as high as 8:1 may be desirable.

For a given dilution ratio, the greater the concentration of the selective solvent component of the dewaxing mixture, the more complete will be the precipitation of wax, and extremely low pour points may often be obtained. However, since the selective solvent has a relatively low solvent power for the oil, the oil-solvent system will in this case form two liquid phases, in addition to the solid wax phase, and the yield of the dewaxed oil will be extremely low. When an excess of solubiilty enhancing solvent is employed, the oilsolvent system will exist as a homogeneous liquid phase, and both pour points and ields of dewaxed oil will be increased. Between these concentrations of solubility enhancing solvents, there is a composition of the combined solvent mixture forming a transition point between the liquid-solid and liquid-liquid-solid phase systems. The transition composition will, of course, depend upon several factors, such as the dilution ratio.

the dewaxing temperature, the specific solventemployed, and the character of the oil, but may be easily determined empirically for any given situation.

We have found that when the volume concentration of the solubility enhancing solvent in the mixed dewaxing solvent is lower than about 10% below the concentration corresponding to the transition composition, the yields of dewaxed oil are reduced quite out of proportion to the improvement in the pour point. Moreover, we have found that the most efiicient dewaxing operations are those which are carried out by employing dewaxing solvent mixtures having compositions near the transition composition, i. e., in which the concentration of the solubility enhancing solvent tall in the range from 10% below to 20% above the transition concentration. Using greater quantities of solubility enhancing agent results in greater yields, but the pour points of the dewaxed oil will often be undesirably high.

Such solvent mixtures as are used in accordance with the present invention may, for example, at temperatures of about F. to 10 F., have complete or substantially complete solubility for oil having specific gravities between 0.90 and 0.941 and refractive indices H13 between 1.50 and 1.52, and substantially no solvent power for wax which is solid at the said temperatures, i. e., not more than a few tenths of one per cent of wax will be dissolved at these temperatures; such an oil may, for example, have a viscosity or between 50 and 55 sec. Say. Univ. at 210 F. Mixtures of solvents having this characteristic may, of course, be used also with oils of different refractive indices, specific gravities or viscosities.

The dewaxing process may also be carried out in several steps, the composition of the solvent mixture being regulated, and the process being carried out as described in the U. S. Patent No. 2, 26,493, dated August 9, 1933.

The yields of dewaxed oil of a given pour point, and the filtration rates can often be further increased by adding a small amount, generally between 0.2% and 1%, of a pour point reducing substance, such as tetrastearyl glucose, pentaerithrite tetrastearate, distearyl picene, cracked residues, metallic soaps, etc, to the oil preferably prior .to chilling. Most of the pour point reducer separates from the oil with the wax, so that it is not normally eiiective to lower the pour point of the filtrate, but is effective to aid in the formation of filterab'le wax crystals.

The following examples illustrate the superior results obtainable with improved solvent mixtures. For comparison, the same oil was dewaxed with several of our solvent mixtures, and with acetone-benzol mixtures, the latter mixture being regarded as standard for dewaxing mineral oils.

Example L-Several samples of a Ventura distillate having a pour point of 95 F. were each diluted with four volumes of various solvent mixtures, heated to produce a homogeneous system, gradually cooled, and filtered at between 0 and 1 C. Diluent compositions and yields are given in percent by volume. The results are shown in the following table: 1

Dilucnt Y m I 1e 0 Exp. dewaxed ggil gg? ig ggg Solubility enhancing fi g oil, F.

percent solvent, percent Fmfuml Ethylene dichloride Furfural OdylnZdch-yde Acchme Bemml .l 94 55 50 5O 92 40 65 35 89 35 75 25 83 3O 0 l0 53 20 *Contained toluene.

With a dilution ratio of 1 to 4, at 0 C., the following compositions of solvent dewaxing mixtures corresponded to the transition point between one and two liquid phase systems; 24% fu'riural, 76% ethylene dichloride; 45% furfural, 55% octylaldehyde; 72% acetone, 28% benzol. It will be noted that in each case the yield dropped oii sharply whenle'ss solubility enhancing solvent was employed than corresponds to the transition point of the solvent in question, with a slight lowering of the pour point, but that with our solvent mixtures we obtain considerably lowerpour points at the transition points :than with the acetone-benzol mixture. We can, therefore, obtain considerably higher yields for a given pour point, and/or lower pour points for a given yield than with the commonly used acetone-benzol mixtures.

Example II.'--The distillate described in Example I was similarly dewaxed with four volumes of a mixture containing 5% furfural and 95% ethylene dichloride, the resulting mixture being heated to 80 C. and filtered at between -19 and 20 C. The dewaxed oil amounted to 82% by volume of the initial oil and had a pour point of F. In a second run, the solvent mixture contained 10% furfural and 90% ethylene dichloride, and 77% of an oil having a pour point of i2.5 F. were obtained. The lowest pour point which could be obtained with acetone-benzol by filtration at -'20 C. was 0 F. In this example, the transition composition was that of the first run, i. e., 5% furfural, 95% ethylene dichloride.

Example III.The distillate described in Example I was similarly dewaxed with four volumes of a mixture containing 25% furfural and 75% octylaldehyde, the resulting mixture being heated to between 97 C. and 100 C. for aboutan hour, and then filtered at between 19 and -20 O. The dewaxed oil amounted to 89% by volume of the initial oil and had a pour point of, 5 F.

These examples are given only for the purpose of illustrating the eflficiency of our new solvents,

and not by way of limitation. Thus, the oil-s01- vent ratio may be varied within wide limits. The dewaxing may be carried out either as a continuous or as a 'batch process. By the term efiective quantity as used in the claims, We mean a quantity of solvent mixture which will maintain sufiicient oil in solution to produce its substantially complete separation from the wax, which is precipitated, and which will produce an oil-solvent mixture of the desired viscosity.

We claim as our invention:

1. In the process of manufacturing a low pour point lubricating oil from wax-bearing mineral oil substantially as described, the step of treating the oil with a liquid solvent mixture to separate solid wax from the oil, said solvent mixture comprising furfural and ethylene dichloride, at temperatures sufiiciently low to solidify the wax, in such proportions that the resulting solvent mixture has substantially complete solvent action on the oil and substantially no solvent action on the wax at the dewaxing temperature.

2. The process for dewaxing mineral oils which comprises mixing said oil with at least an equal volume .of a solvent mixture consisting of between 10 and furfural and between 35 and ethylene dichloride, chilling the resulting mixture to precipitate wax, and removing the precipitated wax from the oil-solvent mixture by mechanical means.

SIJBREN TIJMSTRA. DONALD S. MCKITTRICK. 

